Radiotelegraph transmitting system



L. M. HULL RADIOTELEGRAPH TRANSMITTING SYSTEM Filed Oct. 16. 1920 5 I ihvenior v Panama May 27, 1924.

UNEFE' star-as RADIOTELEGRAPH TRANSMITTING SYSTEM.

Application filed October 18, 1920. Serial No. 417,405.

To aZZ whom it may concern.

Be it known that I, LEWIS 'M; HULL, a citizen of the United States, residing at Chevy Chase, in the county of Montgomery and State of Maryland, have invented new and useful Improvements in -Radiotelegraph Transmitting Systems, of which the following is a specification.

This invention relates to improvements in radio frequency systems comprising tuned oscillatory circuits, and in particular to systems in which high-frequency alternating-current power is amplified by means of three-electrode electron-tube amplifiers. One object of my invention is to simplify the oscillatory circuits which are associated 'in such systems with electron tubes, by eliminating one ofthe circuit elements previously used. Another object resides in the provision of means for increasing the range .of presonant frequencies obtainable in highfrequency generating systems employing an electron-tube amplifier of massive con-. struction. whose intra-electi'ode capacities are large.

An essential part of every radio-frequency system is an oscillatory circuit comprising the inductive and capacitive elements necessary forestablishing in that circuit a condition of resonance to oscillations of a given frequency. In systems usinsr an electron tube associated with-such an oscillatory circuit I have found that the effective capacity existing between grid and cathode of the tube will at radio frequencies be of sufficient magnitude to be an important factor in establishing the resbnance condition. In fact, by connecting the grid-cathode'circuit of an electron tube directly in the oscillatory circuit, the separate condenser which would otherwise be necessary may be eliminated entirely, and the effective capacity reactance of this gridcathode circuit substituted instead. Besides the advantage of simplification of the oscillatory circuit, other benefits accrue from the elimination of the condenser previously employed. I

Owing to the presence of permanent and with ,the radio-frequency waves produced by the irreducible capacities existing between all the electrodes of a three electrode tube the effective input capacity acting between the grid and cathode of said tubemay be greatly in excess of the self capacity existing between these electrodes alone. This capacity cannot be eliminated without eliminating the electron tube entirely, and affects or determines both the magnitude of the current and the condition of res onance in the associated oscillatory circuit. vBy means of my invention this unavoidable capacity is transformed from a wasteful absorber of electrical power into an essential tuning element, and its use as a tuning element allows a reduction in the minimum capacitive reactance attainable in the oscillatory circuits, thus increasing the maximum frequency to which these circuits are resonant.

The latter object of myinvention is oi 7 particular interest and importance in the case of radio transmitting systems. For purposes of illustration I' have shown my invention as being embodied in a transmitter comprising an eletron-tube genera 7 tor of radio-frequency currents, in such combination with one or more electrontube, amplifiers that the effective input capacity of the amplifying system operative between grid and cathode of the electron-tube amplifier, 'forms the essential capacity element of the tuned oscillatory circuit of said radio-frequency generator. The output "circuit of the amplifying system is operatively coupled a transmission circuit for radiating generator.

The single figure of the drawing represents the circuit connections of a transmitting system comprising my invention.

In this figure an electron tube generator is shown at (1), consisting of the usual plate, grid, and incandescent cathode. (6) is a telegraphic key, (17) is a variable selfinductance, and (16) is a battery. (2) is a second electron tube, of suitable characteristies to serve as an amplifier of highfrequency currents; (10) is a battery for heating the cathode of said amplifier; (5)

is a direct-current generator; (12) and (8) are self-inductance coils possessing, in addition, mutual inductance; (7 and (9) are, respectively, the aerial and ground portions of a transmission circuit of the open antenna type.

Electrical power is supplied to the radio frequency generator (1) from battery (16) The high-frequency currents generatedby this tube may be interrupted, for the purpose of radio-telegraphic signaling, by the key, (6). The electron-tube amplifier (2) is coupled to the antenna or radiating system (7 (8), (9), by the mutual inductance between the coils (12) and (8); the plate circuit of this amplifier is supplied with power by the direct-current generator (5). A tuned oscillatory circuit consisting of capacity and inductance elements connected in parallel is essential to the operation of the generator'(1). This circuit is provided by the self-inductance coil (17) and the effective input capacity between the grid and cathode of the amplifier (2). The frequency of the oscillatory currents maintained by the generator (1) is determined by the sel inductance of this coil (17) and the effective input capacity of the amplifier (2). Vhen the system is in operation a high-frequency alternating current is maintained by the generator (1) in the. oscillatory circuit composed of coil (17) and the grid-cathode capacity of amplifier (2). As a result of this current there is impressed between grid and r cathode of amplifier (2) a high-frequency alternating voltage. This serves as an exciting voltage and produces in the tuned output circuit of the amplifier, comprising antenna (7), (8), (9), and coupling coil 12), a hi h-frequency current of the same form and requency as that supplied by the generator, but of much greater amplitude. The additional power necessary for this magnified high-frequency current is drawn in the usual way from the direct-current generator y means of this arrangement theamplifier (2) is thus made to perform a two-fold function: it provides capacity reactance necessary for the operation of the generator (1), and amplifies the radio-frequency alternating-current power supplied to it from thegenerator (1), producing in the antenna alternating currents of greater electrical power. In practice the frequency of the current supplied by'the generator is made equal to the resonant freguency of the antenna, which in effect comprises a tuned circuit between the inductance (8) and the capacity between aerial (7) and ground In the species 0 my invention shown by this diagram the generating circuit used with the generator 1) is of the type known as the reversed feedback circuit. But it is immaterial which of the various types of masses electron-tube generating circuit is employed to excite the amplifier. Each of the several well-known generating circuits requires a periodic or resonant mesh containing a capacity element. The invention discloses a novel and economical method for providing this capacity and simultaneously amplifying the resulting radio-frequency alternating current, regardless of the type of generating circuit employed to produce this cur rent.

Although ll have described my invention in detail only with reference tto specific transmitting circuits, the utility of the general principle involved, that of tuning an oscillatory circuit by making use of the intra-elect rode capacity an electron tube, it is not limited to such systems. \Vhercver an oscillatory circuit is operatively coupled or connected with an electron tube for purposes of amplification of the radio-frequency currents flowing in that circuit, my invention constitutes an improvement over existing systems inasmuch as it provides the capacity element essential to the oscillatory circuit, by the useful employment of the in herent intra-electrode capacities of the electron tube, which in existing systems are not only useless, but frequently detrimental to efficient operation of the apparatus.

What I claim isf 1. A system for the radiation of electric waves comprising a transmission circuit, an electron-tube amplifier Whose plate-cathode circuit is operatively coupled to said transmission eircuit, and a self-excited electrontube generating system so connected to the grid-cathode circuit of said amplifier that the inherent intra-electrode capacity of said grid-cathode circuit furnishes capacity reactance for the operation of said self-excited electron-tube generating system.

2. Asystem for the radiation of electric waves comprising a transmission circuit, an electron-tube amplifier whose plate-cathode circuit is operatively coupled to said trans mission circuit, and a self-excited clcctrontube generating system so connected to the grid-cathode circuit of said amplifier that the inherent intra-eletrode capacity ofsaid grid-cathode circuit furnishes capacity reactance essential to the operation of said self-excited electron-tube generating system, and means for interrupting the plate-cathode circuit of said generating system for the transmission of radiotelegraphic signals,

3. The system defined by claim 1, in which the self-excited electron-tube generating systemcontains a self-inductance coil connected in the grid-cathode circuit, and a second self-inductance coil connected in the plate-cathode circuit, but possessing mutual inductance with the first, said second inductance coil being also connected in parallel with the capacity reactance furnished by. the

inherent intra-electrode capacity of the gridcathode circuit of the electron-tube amplifier.

4. The system defined by claim '1, in which the self-excited electron-tube generating systern contains a closed plate-cathode circuit, a closed grid-cathode circuit, and a eriodic circuit operatively coupled to sai(. platecathode and grid-cathode circuits, said. periodic circuit consisting of a self-inductance 1 coil connected in parallel with the capacity reactance furnished by the inherent intraelectrode capacity of the grid-cathode circuit of the electron-tube amplifier.

In witness whereof I hereunto subscribe 15 

